The fish were tagged and released at the Snake Trap and observed at Lower Granite Dam, Little Goose Dam, Lower Monumental Dam and McNary Dam. 228 cohorts were analyzed over the 4 year period 1993-1996. The migration period was early April through mid May.
We applied four nested models of increasing complexity to the data:
Model details are provided by Zabel, et al. (1996)*.
* In Model 4, a sixth parameter,(
2), describing the slope of
flow-independent term at its inflection point, is allowed to
vary.
The plots below show observed average travel times versus modeled average travel times to each of the four observation sites for all four models.
corresponds to observations at
Lower Granite Dam.
corresponds to observations at
Little Goose Dam.
corresponds to observations at
Lower Monumental Dam.
corresponds to observations at
McNary Dam.
For the fish analyzed here, the simpler model 2 is supported by the data. The model with the seasonal flow term (model 3) results in a loss of fit relative to the model with the simpler linear flow term (model 2) as the seasonal factor is constrained above zero. If allowed it would reduce to the simpler model 2 but is constrained to avoid a singular matrix during the calibration. This implies these steelhead are not modifying their migration behavior as the season progresses. Model 4 offers no significant improvement in fit over model 2. These fish are BORN to move!
MIN
2